Oh well that's unfortunate. I like series because I like to stick to characters on long journeys, getting to know them and care for them. Only the first book is available on Kindle Unlimited so I guess I just won't bother reading past book 1.
(The one exception to this so far is Malazan, which has so many characters and so many times those bounce around from being in a books to disappearing for 3 books, only to resurface again later. Malazan is fantastic though, and totally worth it. Erikson managed to make me care deeply about characters that we only saw for half a book. It's ridiculous.)